The power of a solvent is generally characterized by the kauri-butanol number, which is the volume in ml at 25° C. of a solvent required to produce a defined degree of turbidity when 20 g of a standard solution of kauri resin are added to n-butanol. This number is equal to 57 for 1,1-dichloro-1-fluoroethane (also known as HCFC-141b).
Besides its good solvent power, HCFC-141b is also characterized by a low surface tension (equal to 19.3 mN/m), which gives it a very good capacity for wetting surfaces. Since the boiling point of HCFC-141b is equal to 32° C., this allows it to evaporate quickly and thus to facilitate the deposition of dissolved products onto substrates. Finally, HCFC-141b has no closed-cup flash point and is therefore a non-flammable solvent.
HCFC-141b thus has properties that give it a good capacity for dissolving many organic compounds, especially silicone oils.
However, on account of its non-negligible action on the ozone layer (ozone degradation potential ODP=0.11), HCFC-141b is subject to major regulations that increasingly target its abolition. Thus, the European regulation on substances that are harmful to the ozone layer (No. 2037/2000) has banned the use of HCFCs (hydrochlorofluorocarbons) such as HCFC-141b in solvent applications since 1 Jan. 2002, except for the fields of aeronautics and aerospace, where the ban will take effect in Europe from 2009.
Document EP 974642 proposes an azeotropic composition of 1,1,1,3,3-pentafluorobutane (known under the name HFC-365 mfc) and of 1,1,1,2,3,4,4,5,5,5-decafluoropentane (known under the name HFC-4310 mee) as replacements for HCFC-141b on account of their absence of effect on the ozone layer. However, the kauri-butanol number of such a composition is much lower than that of HCFC-141b. The kauri-butanol number for HFC-365 mfc is 12, and is equal to 9 for HFC-4310 mee.
A composition comprising from 30% to 70% by weight of 1,1,1,3,3-pentafluorobutane and from 70% to 30% by weight of methylene chloride is moreover known (FR 2 694 942).
Moreover, in the context of environmental protection, the current tendency is towards reducing the emissions of solvent by evaporation. Thus, in many “emissive” applications, i.e. applications for which the solvent is liable to evaporate into the air, solvents that are effective at a temperature lower than room temperature are sought.
The present invention thus provides a composition comprising 1,1,1,3,3-pentafluorobutane, methylene chloride and at least one alcohol containing from 2 to 4 carbon atoms.